I've noticed almost every game I've played online in the past years that most people like to start the game with one of their favorite running plays or defensive coverages/blitzes, which I think is stupid. Unless you're really deceptive with your play-calling, I'm going to remember that you like this play and make sure it doesn't work or comes back to bite you the rest of the night.
I usually start the game out of a base formation, and go for a big pass. Maybe a play-action bomb, a 15-yard comeback, a deep post, something to tell the other team that I'm going to be aggressive and come at you right away. It's the best when you connect on it on the VERY FIRST PLAY, because the defense will think you're just one of those guys that chucks it up at every chance you get.
For the rest of the drive, I like to use unbalanced formations, spread formations, and power formations to see how you like to defend against these things. I then adjust my gameplan accordingly, and the chess match begins.